In recent years, optical resin materials having fluorene structures have been developed for decreasing the thickness and weight of a plastic lens for use in a digital camera, a CCD camera, an optical pickup or the like.
As such a resin, a polycarbonate resin having a fluorene structure (to be sometimes abbreviated as “fluorene PC” hereinafter) has come into the spotlight. This resin has excellent properties such as high heat resistance and high refractivity and is useful as a resin for optical elements. For example, JP-A 6-25398 discloses a fluorene PC containing 41 to 95 mol % of a dihydroxyphenylfluorene unit and having a specific photoelastic constant and a specific viscosity. Since, however, the above fluorene PC has a stiff structure, its flowability is insufficient and its moldability is sometimes a problem in some fields of use.
JP-A 2002-30140 discloses a resin having a polysiloxane structure introduced as a soft segment for improving the moldability of a fluorene PC. Further, JP-A 2005-42021 discloses an example in which other polycarbonate resin is blended with a fluorene PC for improving the moldability thereof.
On the basis of an idea similar to the ideas of these techniques, it is thinkable to blend a fluorene PC with a polyester resin to improve the moldability thereof. However, a polyester resin has poor compatibility to a polycarbonate resin, and when a general-purpose polyethylene terephthalate is blended with a fluorene PC, transparency cannot be maintained for a resin composition obtained, and it is difficult to use this composition as a material for optical use.
Under the circumstances, it is demanded to improve the moldability of a fluorene PC while maintaining advantages of the fluorene PC having excellent properties such as high heat resistance, high refractivity, transparency and the like.